During the past several years, measurement of creatine kinase -MB isoenzyme (CK-MB) in serum has become a very popular assay to distinguish between patients with acute myocardial infarctions (AMI) and those with chest pains of other etiology. CK exists primarily as three isoenzymes: BB, which is present in brain; MB, which primarily exists in heart muscle; and MM, which is present both in heart and skeletal muscles. Current methods for measuring MB include electrophoresis, column chromatography, enzyme inhibition and radioimmunoassay (RIA). Although the above methods are useful in measuring MB in serum, there are inherent limitations of these methods. Electrophoresis and chromatography are not sensitive, and thus precise quantitation of MB at the lower level becomes difficult. Enzyme inhibition and RIA methods, although quite sensitive, may not be specific all the time because they measure B subunit of both MB and BB and also crossreact with the macro-molecular forms of CK. Three commercial kits are available which measure specific MB isoenzyme: two use solid phase sandwich immunoassay technique and the other uses a combination of enzyme inhibition and precipitation methods. Stability of the components, cumbersome methodology and poor sensitivity pose problems in the first method; and the second is a very time-consuming manual method whose complete automation is difficult. For these reasons, DSL in collaboration with the UTHSC at Dallas, will develop an assay which will specifically measure CK-MB in serum without crossreactivity to other forms of CK. The proposed method is to prepare a monoclonal antibody using hybrid cell techniques to the chemically well-defined pure protein antigen, human heart (h) CK-MB. Such monoclonal antibody should be monospecific in terms of binding to a unique determinant on the immunogen molecule, CK-MB, and not be reactive with other forms of CK. This antibody will then be used to develop a simple immunoassay to measure specifically CK-MB in serum.